1. Field of the Invention
The present invention relates to an ink composition, an ink set, and an ink jet recording method.
2. Description of the Related Art
As image recording methods in which an image is formed on a recording medium such as paper based on an image data signal, there are an electrophotographic method, a sublimation-type and fusion-type thermal transfer method, an ink jet method, and the like.
In the ink jet recording method, a printing plate is not required, and an image is directly formed on a recording medium by jetting an ink only to an image forming portion. Therefore, the ink can be used with excellent efficiency, and the running cost is low. Furthermore, in the ink jet method, a relatively cheap printing device is used, the printing device can be compactified, and little noise is generated. As described above, the ink jet method has more various advantages than other image recording methods.
So far, the ink jet recording method has been used mainly in the field of office and home printers. However, in recent years, the ink jet recording method has also been used in the field of commercial printing. In the field of commercial printing, the ink jet recording is required to have swiftness (high speed) greater than that of the ink jet recording method used so far.
However, if the time taken for processing such as drying or fixing after recording is shortened so as to speed up the ink jet recording, the permeation of water or an organic solvent in the ink into a recording medium or drying of the water or the organic solvent fails to keep pace with the recording speed, and as a result, in a state where the recording image remains undried, the next recording medium is stacked on the image. During the commercial printing, images are formed on hundreds to thousands of sheets of recording media at a time, and the recording media having undergone image formation are continuously stacked on each other. Therefore, the phenomena easily occur in which the image formed on a recording medium is transferred to the rear surface of another recording medium stacked thereon or the recording media are stuck together (hereinafter, these phenomena are referred to as “stacker blocking”).
Methods for preventing the stacker blocking are being investigated. For example, JP2011-79901A describes a method for preventing stacker blocking by using an ink set containing resin particles, which contain a water-soluble organic solvent in an amount of equal to or less than 20% by mass and have a glass transition temperature of equal to or higher than 60° C., 4 color inks of YMCK, and at least one color ink among RGB inks.
During the ink jet recording, a phenomenon occurs in which water in the ink breaks hydrogen bonds of cellulose in paper as a recording medium and thus the recording medium is curled after drying. It is known that the curling phenomenon can be avoided by adding a specific compound to the ink. For example, JP1997-176538A (JP-H09-176538A) describes, as curling inhibitors formulated into the ink, 1,3-diemthylurea, imidazolidinone, and butylurea.